Cam follower rocker arm

ABSTRACT

A cam follower rocker arm is provided comprising a body with a U-shape cross section with an intermediate opening at the top of the inverted U-shape and having an outside width less then the inside width of the opening, creating a ledge perpendicular to the body side walls. A roller having a peripheral step on both sides to allow the smaller width at the roller periphery to extend into the body opening with the larger width of the roller maintaining a close running clearance of the roller sides to the inside walls of the body when the roller is assembled in the body.

BACKGROUND OF THE INVENTION

The invention relates to a cam follower rocker arm having a U-shapedbody which, when inverted, has an intermediate opening at the top, aroller positioned inside the body and accessible through the opening,and is mounted on an axle that is secured to the side of the U-shapedbody.

A conventional cam follower rocker arm of the kind described in U.S.Pat. No. 4,825,717 the disclosure of which is incorporated herein byreference and over which the present invention is an improvement. U.S.Pat. No. 4,825,717 includes a U-shaped cross section body with anintermediate opening, the width of which is, the same width as the bodyinside walls. A cam follower roller is positioned between the body sidewalls and opening. The roller when positioned in the body is capturedbetween the side walls and extends into the intermediate opening androtates within. The body of U.S. Pat. No. 4,799,464 describes the use ofrectangular opening for a boat style rocker arm of a U-shaped crosssection. This type of rocker arm differs from the cam follower type inthat in the boat style rocker arm is supported in the center by apedestal having a shank that extends through the window. Theperpendicular ledge in the side walls of the boat style arm is used tocarry loads when operating.

SUMMARY OF THE INVENTION

The invention is distinguishable from the prior art having a body thathas a ledge opening with a width at the outside that is less then theinside width at the body opening creating a ledge perpendicular to thebody side walls. A cylindrical roller has a transition step on both endsof its periphery to allow the smaller width of the roller, whenextended, to extend into the outside window and the larger width tomaintain a close running clearance to the inside walls of the body whenassembled. The ledged opening or window in the portion joining the twovertical sides of the U-shaped body may be formed at top or at thebottom of the U-shaped body. This ledge functions to provide a structurethat improves the rocker arm stiffness as verifiable by using analyticaltools and actual static testing. It would not be desirable to have theledge below the roller outer surface diameter. This would increaserocker arm stiffness but would greatly increase the overall mass andmoment of inertia (rotating mass about a pivot) over conventional camfollower rocker arms. Optimization of stiffness and moment of inertiaare key factures that contribute to overall engine performance.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a typical end pivot over head cam valve train with a camfollower rocker arm, valve stem and hydraulic lash adjuster.

FIG. 2 is a cross section of prior art that shows the components for acam follower rocker arm.

FIG. 3 is a cross section of FIG. 2 taken about the roller center.

FIG. 4 is a cross section of the invention that shows the components fora cam follower rocker arm.

FIG. 5 is a cross section of FIG. 4 taken about the roller center.

DETAIL DESCRIPTION OF THE INVENTION

The rocker arm in accordance with the invention is of the cam-followertype and is made preferably by cold-forming operation and comprises, aone-piece metal body generally convex body having a U-shaped crosssection throughout most of its length with two structurally-integralside walls joined by a perpendicularly positioned wall. The rocker armbody includes a recess formed at one end to receive the upper part of alifter post upon which the rocker arm can pivot and a second recess atthe opposite end of the body adapted to receive the end of a valve stem.A central part of the wall joining the sides of the U-shape body has agenerally rectangular opening. The width or transverse dimension of therectangular opening is less than the width of the top wall so that theopening extends substantially, but not entirely, from one side of therocker arm body to the other.

A cam-contacting roller with a stepped periphery is mounted in the bodyand is rotatably carried by the rocker arm that permits the peripheralcircumferential surface of the stepped roller to be exposed through therectangular body opening to engage a cam. The cam-contacting roller isrotatably mounted on an axle carried by the side walls of the body belowthe rectangular opening. The roller preferably has a multiplicity ofneedle bearings to provide minimal friction.

Referring to the drawing, as shown in FIG. 1 a valve train 10 iscomprised of a cam follower rocker arm 11, a hydraulic lash adjuster 12which engages the cam follower rocker arm 11 at one end, a valve stem 13which contacts the opposite end of the cam follower rocker arm 11 and acam 14 located between the hydraulic lash adjuster 12 and valve stem 13is also in contact with the cam follower rocker arm 11. The valve stem13 extends upwardly from a cylinder head (not shown) through a coiledcompression spring 15 which is conventionally seated against thecylinder head and a retaining ring 16 mounted on the valve stem 13. Thecam 14 is able to rotate. The rotating motion of the cam 14 istransmitted through the cam follower rocker arm 11 which pivots aboutthe hydraulic lash adjuster 12 and moves the valve stem 13 in a linearmotion.

In FIG. 2 the cam follower rocker arm 11 is comprised of a U-shape body17 with a vertical surface 18 joined together by a first lower section20 which contacts the valve stem 13 (FIG. 1) and a second lower section21 which engages the hydraulic lash adjuster 12 (FIG. 1). Both lowersections 20, 21 extend perpendicular to the vertical surface 18. Acylindrical roller 22 preferably provided within cylindrical needles 23is mounted on a cylindrical axle 24. The roller 22 contacts the cam 14(FIG. 1) and is located between the vertical surface 18 and extends intoan intermediate rectangular window surface 25. Surfaces 26, 27 extendthrough the lower sections 20, 21 respectively and are wide enough toallow clearance to the roller 22.

As shown in FIG. 3 the window surface 25 is the same width as thevertical surface 18. The roller end surface 28 and the vertical surface18 essentially have a total clearance throughout of about 0.2-0.8 whenassembled. The roller outer periphery 29 and roller end (corner) surface28 extend into the rectangular window surfaces 25, 26 (FIG. 2) and 27(FIG. 2) with clearance.

In FIG. 4 the invention for a cam follower rocker arm 11 is comprised ofa U-shape body 17 a with vertical side surfaces 18 a joined together bya lower section 20 a which has an end that contacts the valve stem 13(FIG. 1) and an opposite end which engages the hydraulic lash adjuster12 (FIG. 1). The lower section 20 a is perpendicular to the verticalsurface 18 a. A cylindrical roller 22 a and cylindrical needles 23 aremounted on a cylindrical axle 24. The roller 22 a contacts the cam 14 inFIG. 1 and is located between the vertical surface 18 a and anintermediate rectangular window surface 25 a. Surfaces 26 a, 27 a extendthrough the lower section 20 a and are wide enough to allow clearance tothe roller 22 a.

In FIG. 5 the window surface 25 a is smaller then the vertical surface18 a creating a ledge that has a minimum distance of 30% materialthickness. The roller 22 a has a transition surface 30 a on both endsthat allows a total clearance of 0.2-0.8 between the vertical surface 18a and the roller end surface 28 a. The roller outer surface 29 a androller transition surface 30 a extend into the rectangular windowsurfaces 25 a, 26 a (FIG. 4) and 27 a (FIG. 4) with clearance.

Although the present invention has been described in terms of specificembodiments, the invention is not meant to be so limited. For example,while the preferred body configuration comprises a generally U-shapecross section, the body also need no be so limited. Various additionalchanges can be made to the proportions and arrangement of the parts usedwhile still obtaining the benefits of the invention. Thus the inventionis only to be limited by the scope of the appended claims.

1. A cam follower rocker arm comprised of a generally U-shaped bodyhaving sidewalls with a roller opening joining the sidewalls, a rollerwith an axle for mounting the roller in the sidewalls of the body at theopening and wherein the body opening is formed with a ledge having anarrower width and perpendicular to the body sidewall and the roller isformed with steps providing a relative small peripheral width to conformwith said ledge.
 2. The cam follower of claim 1 wherein the ledge of thebody permits access solely to the smaller width of said rollerperiphery.
 3. A U-shaped cross section body of claim 1 with anintermediate window opening that is less then the body inside widthcreating a ledge perpendicular to the body side walls.
 4. A roller ofclaim 1 with a transition on both sides to allow the smaller width toextend into the window of claim 2 and the larger width to maintain aclose clearance to the inside walls of the body of claim
 2. 5. Aninverted U-shaped cross section body of claim 1 with an intermediatewindow opening that is less then the body inside width creating a ledgeperpendicular to the body side walls.
 6. A roller of claim 1 that usesspacers (not shown) on either side of the roller to allow the roller toextend into the window of claim 2 and the stack-up of the roller andspacers maintain a close clearance to the inside walls of the body ofclaim 2.